1. Field of the Invention
The present invention relates to an engine mounted on a vehicle, such as a utility vehicle.
2. Description of the Prior Art
In engines mounted on various vehicles, such as a utility vehicle, a mechanism is provided in which an endless transmission belt, such as a chain, is stretched between a drive sprocket for a crankshaft journaled on a crankcase and a driven sprocket secured to driven shafts, such as a camshaft and a pump drive shaft, journaled on the crankcase, and the power of the crankshaft is transmitted to the driven shafts, such as the camshaft and the pump drive shaft.
FIG. 7 shows an outline of a winding power transmission unit 200 in which a conventional chain 206 is used. In FIG. 7, the chain 206 is stretched between a drive sprocket 202 secured to a crankshaft and a driven sprocket 204 secured to a pump shaft. When the drive sprocket 202 is rotated counterclockwise as shown in the figure, the upper section 206a of the chain 206 is stretched and becomes a tension side, and the lower section 206b is released and becomes a loose side.
The winding power transmission unit 200 shown in FIG. 7 is equipped with a chain guide 208 for applying tension to the lower section 206b (loose side) of the chain 206. One end section 208a of the chain guide 208 is swingably supported on the wall section 211 of the crankcase 210 in the vicinity of the lower section of the driven sprocket 204, and the other end section 208b of the chain guide 208 becomes a free end. The chain guide 208 extends along the lower section 206b on the loose side. Furthermore, a chain tensioner 220 is disposed below the other end section 208b of the chain guide 208, and the pressing piece 224 of the chain tensioner 220 presses the other end section 208b of the chain guide 208 toward the lower section 206b of the chain 206.
The chain tensioner 220 shown in FIG. 7 is equipped with a nearly cylindrical housing 222, the pressing piece 224 slidably loaded inside the housing 222, and a coil spring 226 for biasing the pressing piece 224 toward the lower section 206b of the chain 206. The housing 222 of the chain tensioner 220 shown in FIG. 7 has a flange section 232, has a male screw section 234 above the flange section 232 and has a hexagon bolt-shaped head section 228 below the flange section 232. Furthermore, in the wall section 211 of the crankcase 210, a female screw hole 214 screw-engaged with the male screw section 234 of the flange section 232 is formed. The chain tensioner 220 shown in FIG. 7 is screwed to the wall section 211 of the crankcase 210 via an O-ring 230 disposed between the flange section 232 of the housing 222 and the wall section 211 of the crankcase 210.
The chain tensioner 220 according to the conventional technology shown in FIG. 7 is equipped with a plurality of components, such as the pressing piece 224, and requires the O-ring 230 for allowing the chain tensioner 220 to be installed in the wall section 211 of the crankcase 210 in a hermetically sealed state, whereby the number of components is large and the cost is raised. Furthermore, it is necessary to form a machined seat for allowing the chain tensioner 220 to be screwed to the wall section 211 of the crankcase 210 while ensuring hermetic sealing inside the crankcase 210. In other words, it is necessary to form the male screw section 234 of the flange section, to form the female screw hole 214 in the wall section 211 of the crankcase 210 and to form a flat section for allowing the O-ring 230 to perform sealing. Hence, there are problems, such as cost increase due to increase in processing man-hour and high susceptibility to design restrictions.
In addition, a guide mechanism in which a plurality of guide units for guiding the traveling of a ring-shaped belt stretched between at least two rotation shafts while applying tension to the ring-shaped belt are connected mutually in a swingable state is disclosed as another conventional example in Japanese Patent Application Laid-open Publication No. 2002-89636.
The guide mechanism disclosed in Japanese Patent Application Laid-open Publication No. 2002-89636 requires a connection structure for connecting the plurality of guide units. Hence, there are problems that the overall structure of the guide mechanism becomes large and it becomes difficult to securely obtain sufficient installation space for the guide mechanism and that the installation of the guide mechanism is complicated.